Yes but no. You're absolutely right on your three points, esp. the 3rd that states that proving an MAE is
an extremely high bar that is basically never met.
But! There's another way out for Musk.
Merger agreements include covenants, promises that the parties make to one another about what they will do to close the deal. If one of the parties can prove that the other didn't fulfill a covenant obligation and therefore broke its promise to work towards closing in good faith, then that's a valid justification to walk away.
The merger agreement includes covenants that force Twitter to provide any and all information "reasonably" requested by Musk, in a timely manner.
So the game becomes: how to trick Twitter into not respecting its obligations? One way is to ask for information that is impossible to provide: "Give me all the tweets since the beginning of time, each tweet on a single piece of paper!"
But Twitter might object, and a judge might find, that this is done in bad faith...
The other, more subtle way is to ask for information that Twitter should be very anxious and reluctant to provide, such as, for example, personal information regarding users. Twitter may run afoul of many regulations if it does, and has reasons to believe Musk won't honor any NDA he might sign (as he has a history of disrespecting his own word). Yet on the other hand, Musk can argue that he's entitled to ask for such information.
That's the nature of the current game. I don't think there's any way this isn't settled in court.
Note: for more on this, cf. Matt Levine's newsletter from June 6th.